Originally posted by Spodeworld OK. I assume that the reading is valid for when the flash is facing forward, but if it is facing away, the thyristor would not be aware of that and would not compensate for the additional power required when bouncing or modifying the flash.
Of course. But the flash head, at the top of the flash unit, points independently of the flash body, which contains the still-forward-facing photocell that controls the thyristor. Pointing the photocell anywhere other than towards the subject makes no sense. The flash head does its bounce thing without forcing the photocell to point away from the subject.
Regardless of where the flash head is pointing, or how the light is modified, the photocell (still aimed at the subject) forces the thyristor-controlled flash tube to keep emitting light until the subject has received enough light to satisfy the photocell that is looking at the light coming from the subject towards the camera (assuming on-camera flash). Then the lens aperture determined by the red or green auto mode will give the "correct" exposure (for a "middle gray" subject).
Note that the flash unit does ALL the "auto" part, while the camera has its aperture manually set to the value read off the back of the flash unit.
If the flash is not on-camera, or if there is significant ambient light, the situation gets more complicated, and the flash unit has no additional smarts to deal with this. That's what TTL works to fix. But the A280-T flash does not do any TTL with our digital cameras. Worked nicely with my film LX.